The increase in the world population and consequent increase in industrial capacity has created the important problem of disposing of the resulting and ever-increasing quantities of waste without disturbing the existing ecological balance.
It is a well known practice to store solid waste in gas- and water-tight containers underground, as for example in abandoned salt mines. Liquid waste can only be disposed of in this way, if it has been solidified beforehand using appropriate means.
Storing waste materials, for example salt residues from the treatment of mined crude potash salts, in heaps and piles above ground is also known. However, considerable technical complexity is involved in sealing off the subsoil and collecting and diverting the surface water to prevent salinization of the soil and ground water. In order to keep the area of such heaps and piles from becoming literally mountains, German patent application No. 26 14 238 published Oct. 13, 1977 outlines a process for piles of bulk materials, particularly residues from the treatment of crude potash salts, by which it is possible to produce such piles of great height over a relatively small area.
Using other well-known processes, liquid waste, particularly waste lye from treatment of crude potash salts, can be injected into the absorbent deeper rock strata, for example, sandstone or sheet dolomite. However, this requires high injection pressures and, consequently, considerable energy. Moreover, the available capacity at any given time cannot be checked directly.
Another method of disposal is ocean incineration, particularly of those materials containing halogens, so that the resulting hydrogen halides are absorbed by the sea water and bound by its carbonate component with the liberation of carbon dioxide. It is also common to dump acidic liquid waste, such as dilute acid in the ocean. Over prolonged periods, these processes dispose of waste, but alter negatively the existing ecological and biological balance of the ocean.
According to German patent application No. 22 25 664, published Dec. 6, 1973, liquid radioactive waste or solid radioactive waste with good flow properties is mixed above ground with cement or bitumen to yield a slurry which is fed into underground cavities where it solidifies. As a result of their radioactivity, these wastes require a large number of added substances in order to dilute the radioactive waste, to a large extent, in addition to causing solidification. This means that a large volume of space is required for storage of a small quantity of waste.
German Patent No. 25 49 313 published May 5, 1977, describes a process in which liquids stored in underground cavities are recovered with a mixture of styrene, cyclohexanol peroxide, and cobalt accelerator, which hardens to produce a coating which prevents possible release of gases from the stored liquid. However, this does not exclude the possibility of a reaction between the stored liquids and the salt of the cavity wall, thereby generating gases which ultimately rupture the coating.
The problem then was to find a method of storing liquid waste in the cavities produced in natural salt deposits by solution mining, hereafter referred to as the storage area, without gases being produced due to the waste material reacting with the salt in the deposit.